In ink jet printers of the type shown in U.S. Pat. No. 3,500,436 granted on Mar. 10, 1970, to R. W. Nordin, pressurized ink on the order of approximately 20 to over 100 psi is delivered to nozzles on the order of 0.001-inch or less in orifice diameter in order to print indicia on paper. Any particle of dust trapped in the fluid ink will clog such a nozzle. The provision of suitably clean and filtered ink has heretofore been exceedingly difficult and unreliable.
U.S. Pat. No. 3,393,988 granted on July 23, 1968, to J. Blumenthal shows a method of forming a minature nozzle from a glass tube by heating one end of the tube until the annular portion converges and essentially blocks the entire central passage through the tube. The heated end, after cooling, is ground until a microscopic orifice is opened, thereby forming a very small nozzle for an ink jet printer.
It has been found that no matter how much a nozzle is washed and no matter what filter is used and fastened to the input of the nozzle, the nozzle still has a high statistical likelihood of clogging due to the ingress of particles after cleaning or during assembly of the nozzle and the filter. This greatly increases the amount of scrap, increases manufacturing complexity with resultant drastic increase in cost of manufacture of nozzles for ink jet printers.
The process of making filters using sintered ground glass or frit is well-known in the prior art and is mentioned as being current practice in the Sept. 12, 1963, issue of Machine Design magazine on page 184. In this process ground particles of glass are formed and may be divided by common screening technique into various grit sizes and can be used to produce porous glass filters.
The ground and screened particles are mixed with a liquid vehicle or binder and are pressed to the desired shape. After the vehicle is dried, the part is heated until the glass particles soften and fuse together. If a porous material is desired, the firing is carried out only to the point where the particles start to fuse. The resulting product is a network of pores classified by the maximum pore diameter which is controllable down to very small sizes.
It is an object of the present invention to produce a nozzle which has a high propensity to remain open and unclogged in spite of the possible presence of particles larger than the diameter of the orifice.
It is another object of the present invention to filter out all of the particles of a size larger than the diameter of the orifice of the nozzle prior to delivery of the particles to the nozzle orifice.
It is a further object of the present invention to provide methods of making a combined nozzle and filter with a high likelihood of cleanliness and absence of large diameter particles between the filter and the nozzle.